1. Field of Invention
The present invention relates to a method for fabricating thin film transistors (TFTs) and pixel structures, and particularly to a method for fabricating low temperature polysilicon (LTPS) TFTs and LTPS pixel structures.
2. Description of Related Art
Nowadays, benefiting from fast development of optoelectronic technology and semiconductor technology, the video and image devices are now becoming lighter and slimmer. Notwithstanding a few advantages they still has, cathode ray tube (CRT) displays are limited by their large bulk and radiations that to some degree hurt human eyes. Flat panel displays, including liquid crystal displays (LCDs), have advantages such as thinner configuration, lighter weight, lower operation voltage, less power consumption, all colorization and lower radiation, thus becoming a mainstream of the display market in the 21 century.
LCDs are generally categorized into an active matrix type and a passive matrix type, according to driving methods thereof. An active matrix type LCD usually uses thin film transistors (TFTs) as driving switches. TFTs are generally categorized into amorphous silicon TFTs and poly-silicon TFTs, according to materials adopted for making channel layers thereof.
Previous poly-silicon TFTs were generally fabricated under a relative high temperature up to 1000° C., due to which only limited quantity of materials can be selected for making substrates. However, the development of laser technology makes it possible to fabricate poly-silicon TFTs under a lower temperature up to 600° C., which is called low temperature poly-silicon TFTs (LTPS-TFTs).
LTPS-TFTs have many advantages that amorphous silicon TFTs do not have, such as high aperture ratio, high resolution, and excellent display quality, as well as capability of integrating a driving integrated circuit onto a glass substrate. Unfortunately, a process for fabricating LTPS-TFTs is much more complicated and need more steps of mask processing than a process for fabricating amorphous silicon TFTs which usually requires five steps of mask processing. Fabricating typical complementary LTPS-TFTs require eight steps or nine steps of mask processing, which cost much. Therefore, what is needed is to simplify current mask processing for the LTPS-TFTs.